The fuel cell power generator mainly includes: a hydrogen generator configured to generate a produced gas containing a high concentration of hydrogen; and a fuel cell configured to generate electric power by using hydrogen generated by the hydrogen generator.
The hydrogen generator includes: a reforming unit configured to generate a reformed gas containing hydrogen, methane, carbon monoxide (in an amount of about 10 to 15%), carbon dioxide and steam by subjecting a raw gas and steam to steam-reforming reaction using a reforming catalyst in which a hydrocarbon fuel, such as a town gas and an LPG, is used as the raw gas; and a CO elimination unit configured to eliminate carbon monoxide exhibiting poisoning action to a fuel cell from the reformed gas.
When a proton exchange membrane fuel cell is used as a fuel cell, a concentration of carbon monoxide contained in the reformed gas is required to be eliminated to about 10 ppm. Generally, the CO elimination unit includes two-stage units which includes: a conversion unit configured to eliminate carbon monoxide to about 0.5% by shift reaction using a conversion catalyst; and a selective oxidation unit configured to mix carbon monoxide and oxygen by using a selective oxidation catalyst, thereby oxidizing carbon monoxide through selective oxidation reaction and reducing the concentration of CO to 10 ppm or less.
From the viewpoint of a reduction of the size, enhancement of efficiency, enhancement of a start-up characteristic, enhancement of driving stability, and a cost reduction attributable to simplification of a structure, various devices is proposed as a hydrogen generator. As an example thereof, in order to realize a compact, highly efficient hydrogen generator, there is provided a hydrogen generator including a reforming unit and a CO elimination unit which are integrated and also a water evaporation unit which is provided integrally adjacent to a catalyst layer rather than being provided outside the hydrogen generator. According to the structure, an optimum heat balance and stable operation are achieved while heat in the hydrogen generator is utilized to the maximum level, thereby reducing the size of the structure of the hydrogen generator and also reducing cost of the hydrogen generator.
However, when an operating state of the hydrogen generator (for example, power generation load on a fuel cell in a hydrogen generator built in a fuel cell system) changes, an amount of hydrogen to be generated is reduced or increased by changing a raw material supply amount and a water supply amount. When the water supply amount is changed from a small amount to a large amount, a larger amount of water is fed to the water evaporation unit.
The water evaporation unit is configured to balance so as to evaporate water by heat of a combustion exhaust gas from a burner surrounding the water evaporation unit and heat of a catalyst layer. However, when a large amount of water is suddenly supplied, the supplied water is not fully evaporated according to circumstances, whereby some of unvaporized water may be supplied to a reforming catalyst in the form of a droplet.
When the droplets are supplied to the reforming catalyst, the droplets absorb latent heat of the reforming catalyst during evaporation of the droplets, so that the temperature of the reforming catalyst locally and suddenly falls. The temperature fall also induces a fall in the temperature of the catalysis located in surrounding areas. As a result, the transforming catalyst as a whole can not maintain a stable temperature state thereof, which may cause fluctuations in the amount of hydrogen generated.
In the catalyst supplied with the droplets, an instantaneous temperature fall, so that the catalyst may receive thermal shock, and cracking or exfoliation may occur. Accordingly, in a related-art structure, a second evaporation unit is provided in a lower portion of a downstream side of the water evaporation unit, and a partition wall is provided on the lower portion and the side portion of the second evaporation unit. According to the structure, even if droplets are ejected from the evaporation unit, the droplets will be trapped by the lower portion of the second evaporation unit, and only the steam generated by evaporating droplets which have been trapped is sent from the second evaporation unit (see, for example, Patent Document 1).